The invention relates to an electrical machine, preferably an alternator for motor vehicles, comprising a rectifier assembly according to the preamble of claim 1.
In the case of alternators for motor vehicles, a rectifier assembly is usually located on the rear end face of the alternator that is driven by the motor vehicle, which said rectifier assembly rectifies the three-phase alternating voltage generated in the stator winding of the alternator to charge a storage battery in the electrical system of the motor vehicle. The rectifier bridge circuit of the assembly is composed of a plurality of diode bridges, each having a positive diode and a negative diode connected in series. The negative diodes are fixed to and contacted with a common negative connecting plate on the anode side, and the positive diodes are fixed to and contacted with a common positive connecting plate on the cathode side, said negative and positive connecting plates being configured as negative and positive cooling bodies, respectively. Each of the free winding terminations of the diodes is connected to the individual diode bridges via an additional circuit connection, and each one is connected on the input side with a phase connection of the stator winding.
A means of attaining the object of the invention is made known in U.S. Pat. No. 4,606,000, in which the negative and positive connecting plates lie on top of one another, insulated, in the manner of a sandwich, and they are fixed to the front face of the rear end shield of the alternator. The cooling bodies are displaced relative to each other in the region of their diodes in such a manner that the diode connections for establishing the circuit connections are accessible from the exterior. To evacuate the dissipated heat in the rectifier assembly, the two cooling bodies are expanded to cover a large area, with the negative cooling body resting on the end shield, and the dissipated heat from the negative diodes being given off to the end shield of the machine by thermal conduction. The dissipated heat from the positive diodes is given off to the cooling air that flows through the machine there, said dissipated heat being given off substantially via the positive cooling body in a region of the cooling body equipped with ventilation slots.
The known means for attaining the object of the invention have the disadvantage that, by configuring the connecting plates as cooling bodies, the rectifier assembly has relatively large dimensions, so that only a minimal degree of freedom remains for attaching the rectifier assembly on the front face of the rear end shield. Furthermore, the end shield of the machine must be fabricated out of material having good thermal conduction properties, since a majority of the dissipated heat is first directed by means of thermal conduction to the end shield, where it is carried out by the stream of cooling air from the rear fan of the machine by means of radiation and convection. Additionally, the relatively great masses of the cooling bodies pose a risk; namely that, if vibrations or jarring occurs between the rectifier parts and between them and the end shield, small relative motions can set in that can result in interruptions in the rectifier bridge circuit.
The aim of the means provided by the present invention is to evacuate the dissipated heat from the rectifier assembly to the cooling air of the machine in the most efficient manner possible, in order to keep the dimensions of the rectifier assembly as small as possible.
In contrast to the prior art, the electrical machine according to the invention having the characterizing features of claim 1 has the advantage that the dissipated heat from the rectifier assembly is substantially taken up by the cooling air drawn in by the fan of the machine before it is heated further by the dissipated heat from the machine. By efficiently cooling the rectifier assembly, the dimensions of said rectifier assembly can be reduced, resulting in greater degrees of freedom when it comes to attaching the rectifier assembly to the end shield. The dissipated heat from the front connecting plate of the rectifier assembly is evacuated by a cooling body to the cooling air flowing into the end shield in the vicinity of the shaft. A further advantage lies in the fact that, due to the small dimensions of the rectifier assembly, said rectifier assembly can be inserted in a window in the end shield, so that its rear connecting plate extends to a point where it is situated close in front of the vanes of the rear fan of the machine, so that, from there, it can give off the dissipated heat to the cooling air flowing radially outwardly with strong force.
The measures listed in the dependent claims result in advantageous further developments and improvements of the features indicated in the main claim. For example, to attain small dimensions of the rectifier assembly, said rectifier assembly is combined in a bridge circuit to form a compact diode module by the fact that the negative and positive diodes of each diode bridge are composed of semiconductor substrates that, together with a connecting piece inserted therebetween, forms a stack that is located between a positive connecting plate and a negative connecting plate. As a result, the additional components typically required to connect diode bridges are eliminated. In an advantageous further development, the stacks between the two connecting plates are arranged adjacent to each other, and their connecting pieces extend adjacently outward on a longitudinal side of the diode module for connection to the stator winding. There, the ends of the stator windings can be connected directly, so that the additional circuit connections required until now can be eliminated, especially since these circuit connections were usually embedded in plastic; this poses a potential fire hazard if short circuits occur. In order to enable the easiest possible connection of the stator winding from the exterior after the rectifier assembly is installed, the connecting pieces are angled on the longitudinal side of the diode module in such a manner that their end sections extend outwardly in a recess of the cooling body for connection of the stator winding.
To attain an even distribution of the heat dissipated from the diode module to the cooling body, the invention provides that said cooling body is configured semicircular in shape and is screwed into a fixed position from the exterior on the front face of the end shield. To enable good evacuation of dissipated heat from the cooling body to the cooling air of the machine, said cooling body is equipped in advantageous fashion with adjacently arranged, radially extending cooling fins on its exterior side furthest from the diode module. In order direct the cooling air drawn in by the fan of the machine radially from the exterior to the inside past the cooling body before it enters the orifices of the end shield, air intake openings are provided in the vicinity of the shaft in the protective cap known per se that covers the front face of the end shield, said air intake openings preferably being distributed around the entire circumference of the protective cap, but that are at least arranged above the cooling body.
When the stator winding is connected directly to the connecting pieces of the diode module, the star connections are located on the rear winding head of the machine, when a star connection is involved. As an alternative, the invention provides that the stator winding and the connecting pieces of the diode module are interconnected via an electrical connector containing the corresponding connecting conductors. The advantage of this is that the star connection of the stator winding can also be moved away from the winding head into electrical connector, especially since the neutral point is then connected in simple fashion via a further diode bridge of the diode module to utilize the harmonic waves of the voltage generated in the stator winding. In order to attach the electrical connector to the front face of the end shield in a manner that allows it to be as protected and vibration-resistant as possible, the invention provides that it is inserted between the cooling body and the end shield.
The cooling body is attached to either the positive connecting plate or the negative connecting plate, that is, it is screwed on, welded on, or riveted on. In the first case, the rectifier assembly is fixed to the cooling body in two dimensions by the outside of its positive connecting plate, and the cooling body is equipped with a positive terminal for connection to the vehicle electrical system battery of the motor vehicle. The cooling body with an electrically insulating intermediate layer is fixed to the end shield that carries the ground potential of the vehicle electrical system. In an advantageous further development, a thermally conductive material, e.g., high-alumina ceramics, is used for the electrically insulating intermediate layer, so that part of the heat dissipated from the cooling body can also be evacuated to the end shield as an additional heat sink. To attach the cooling body to the end shield, mounting holes are advantageously provided in the cooling body, into which insulating sleeves are inserted that accommodate the fastening screws of the cooling body. In order to connect the negative connection of the rectifier assembly to ground potential in this exemplary embodiment, the outside of the negative connecting plate is advantageously connected with a bus bar in two dimensions, which said bus bar, as ground connection, extends across the opening on the inside of the end shield and is fixed to the end shield by its ends.
In the alternative exemplary embodiment, the rectifier assembly is connected in two dimensions to the cooling body by the outside of its negative connecting plate, said cooling body, in turn, being fixed to the end shield representing the ground potential in an electrically and thermally conductive manner. A stronger evacuation of the dissipated heat from the cooling body to the end shield as additional heat sink can be attained in advantageous fashion by the fact that the cooling body rests against the end shield in two dimensions, preferably over an electrically and thermally conductive intermediate layer. A paste, an adhesive, or a wax, among other things, can be used as thermally conductive intermediate layer.
To save components, the cooling body can also be an integral part of the positive and/or negative connecting plates.
The exposed connecting plate furthest from the cooling body can be cooled intensively by ensuring that its outside at least nearly coincides with the inside of the end shield in the region of the opening in the front face.